1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Telemetry communication for Wilco EC
4 *
5 * Copyright 2019 Google LLC
6 *
7 * The Wilco Embedded Controller is able to send telemetry data
8 * which is useful for enterprise applications. A daemon running on
9 * the OS sends a command to the EC via a write() to a char device,
10 * and can read the response with a read(). The write() request is
11 * verified by the driver to ensure that it is performing only one
12 * of the allowlisted commands, and that no extraneous data is
13 * being transmitted to the EC. The response is passed directly
14 * back to the reader with no modification.
15 *
16 * The character device will appear as /dev/wilco_telemN, where N
17 * is some small non-negative integer, starting with 0. Only one
18 * process may have the file descriptor open at a time. The calling
19 * userspace program needs to keep the device file descriptor open
20 * between the calls to write() and read() in order to preserve the
21 * response. Up to 32 bytes will be available for reading.
22 *
23 * For testing purposes, try requesting the EC's firmware build
24 * date, by sending the WILCO_EC_TELEM_GET_VERSION command with
25 * argument index=3. i.e. write [0x38, 0x00, 0x03]
26 * to the device node. An ASCII string of the build date is
27 * returned.
28 */
29
30 #include <linux/cdev.h>
31 #include <linux/device.h>
32 #include <linux/fs.h>
33 #include <linux/mod_devicetable.h>
34 #include <linux/module.h>
35 #include <linux/platform_data/wilco-ec.h>
36 #include <linux/platform_device.h>
37 #include <linux/slab.h>
38 #include <linux/types.h>
39 #include <linux/uaccess.h>
40
41 #define TELEM_DEV_NAME "wilco_telem"
42 #define TELEM_CLASS_NAME TELEM_DEV_NAME
43 #define DRV_NAME TELEM_DEV_NAME
44 #define TELEM_DEV_NAME_FMT (TELEM_DEV_NAME "%d")
45 static struct class telem_class = {
46 .name = TELEM_CLASS_NAME,
47 };
48
49 /* Keep track of all the device numbers used. */
50 #define TELEM_MAX_DEV 128
51 static int telem_major;
52 static DEFINE_IDA(telem_ida);
53
54 /* EC telemetry command codes */
55 #define WILCO_EC_TELEM_GET_LOG 0x99
56 #define WILCO_EC_TELEM_GET_VERSION 0x38
57 #define WILCO_EC_TELEM_GET_FAN_INFO 0x2E
58 #define WILCO_EC_TELEM_GET_DIAG_INFO 0xFA
59 #define WILCO_EC_TELEM_GET_TEMP_INFO 0x95
60 #define WILCO_EC_TELEM_GET_TEMP_READ 0x2C
61 #define WILCO_EC_TELEM_GET_BATT_EXT_INFO 0x07
62 #define WILCO_EC_TELEM_GET_BATT_PPID_INFO 0x8A
63
64 #define TELEM_ARGS_SIZE_MAX 30
65
66 /*
67 * The following telem_args_get_* structs are embedded within the |args| field
68 * of wilco_ec_telem_request.
69 */
70
71 struct telem_args_get_log {
72 u8 log_type;
73 u8 log_index;
74 } __packed;
75
76 /*
77 * Get a piece of info about the EC firmware version:
78 * 0 = label
79 * 1 = svn_rev
80 * 2 = model_no
81 * 3 = build_date
82 * 4 = frio_version
83 */
84 struct telem_args_get_version {
85 u8 index;
86 } __packed;
87
88 struct telem_args_get_fan_info {
89 u8 command;
90 u8 fan_number;
91 u8 arg;
92 } __packed;
93
94 struct telem_args_get_diag_info {
95 u8 type;
96 u8 sub_type;
97 } __packed;
98
99 struct telem_args_get_temp_info {
100 u8 command;
101 u8 index;
102 u8 field;
103 u8 zone;
104 } __packed;
105
106 struct telem_args_get_temp_read {
107 u8 sensor_index;
108 } __packed;
109
110 struct telem_args_get_batt_ext_info {
111 u8 var_args[5];
112 } __packed;
113
114 struct telem_args_get_batt_ppid_info {
115 u8 always1; /* Should always be 1 */
116 } __packed;
117
118 /**
119 * struct wilco_ec_telem_request - Telemetry command and arguments sent to EC.
120 * @command: One of WILCO_EC_TELEM_GET_* command codes.
121 * @reserved: Must be 0.
122 * @args: The first N bytes are one of telem_args_get_* structs, the rest is 0.
123 */
124 struct wilco_ec_telem_request {
125 u8 command;
126 u8 reserved;
127 union {
128 u8 buf[TELEM_ARGS_SIZE_MAX];
129 struct telem_args_get_log get_log;
130 struct telem_args_get_version get_version;
131 struct telem_args_get_fan_info get_fan_info;
132 struct telem_args_get_diag_info get_diag_info;
133 struct telem_args_get_temp_info get_temp_info;
134 struct telem_args_get_temp_read get_temp_read;
135 struct telem_args_get_batt_ext_info get_batt_ext_info;
136 struct telem_args_get_batt_ppid_info get_batt_ppid_info;
137 } args;
138 } __packed;
139
140 /**
141 * check_telem_request() - Ensure that a request from userspace is valid.
142 * @rq: Request buffer copied from userspace.
143 * @size: Number of bytes copied from userspace.
144 *
145 * Return: 0 if valid, -EINVAL if bad command or reserved byte is non-zero,
146 * -EMSGSIZE if the request is too long.
147 *
148 * We do not want to allow userspace to send arbitrary telemetry commands to
149 * the EC. Therefore we check to ensure that
150 * 1. The request follows the format of struct wilco_ec_telem_request.
151 * 2. The supplied command code is one of the allowlisted commands.
152 * 3. The request only contains the necessary data for the header and arguments.
153 */
check_telem_request(struct wilco_ec_telem_request * rq,size_t size)154 static int check_telem_request(struct wilco_ec_telem_request *rq,
155 size_t size)
156 {
157 size_t max_size = offsetof(struct wilco_ec_telem_request, args);
158
159 if (rq->reserved)
160 return -EINVAL;
161
162 switch (rq->command) {
163 case WILCO_EC_TELEM_GET_LOG:
164 max_size += sizeof(rq->args.get_log);
165 break;
166 case WILCO_EC_TELEM_GET_VERSION:
167 max_size += sizeof(rq->args.get_version);
168 break;
169 case WILCO_EC_TELEM_GET_FAN_INFO:
170 max_size += sizeof(rq->args.get_fan_info);
171 break;
172 case WILCO_EC_TELEM_GET_DIAG_INFO:
173 max_size += sizeof(rq->args.get_diag_info);
174 break;
175 case WILCO_EC_TELEM_GET_TEMP_INFO:
176 max_size += sizeof(rq->args.get_temp_info);
177 break;
178 case WILCO_EC_TELEM_GET_TEMP_READ:
179 max_size += sizeof(rq->args.get_temp_read);
180 break;
181 case WILCO_EC_TELEM_GET_BATT_EXT_INFO:
182 max_size += sizeof(rq->args.get_batt_ext_info);
183 break;
184 case WILCO_EC_TELEM_GET_BATT_PPID_INFO:
185 if (rq->args.get_batt_ppid_info.always1 != 1)
186 return -EINVAL;
187
188 max_size += sizeof(rq->args.get_batt_ppid_info);
189 break;
190 default:
191 return -EINVAL;
192 }
193
194 return (size <= max_size) ? 0 : -EMSGSIZE;
195 }
196
197 /**
198 * struct telem_device_data - Data for a Wilco EC device that queries telemetry.
199 * @cdev: Char dev that userspace reads and polls from.
200 * @dev: Device associated with the %cdev.
201 * @ec: Wilco EC that we will be communicating with using the mailbox interface.
202 * @available: Boolean of if the device can be opened.
203 */
204 struct telem_device_data {
205 struct device dev;
206 struct cdev cdev;
207 struct wilco_ec_device *ec;
208 atomic_t available;
209 };
210
211 #define TELEM_RESPONSE_SIZE EC_MAILBOX_DATA_SIZE
212
213 /**
214 * struct telem_session_data - Data that exists between open() and release().
215 * @dev_data: Pointer to get back to the device data and EC.
216 * @request: Command and arguments sent to EC.
217 * @response: Response buffer of data from EC.
218 * @has_msg: Is there data available to read from a previous write?
219 */
220 struct telem_session_data {
221 struct telem_device_data *dev_data;
222 struct wilco_ec_telem_request request;
223 u8 response[TELEM_RESPONSE_SIZE];
224 bool has_msg;
225 };
226
227 /**
228 * telem_open() - Callback for when the device node is opened.
229 * @inode: inode for this char device node.
230 * @filp: file for this char device node.
231 *
232 * We need to ensure that after writing a command to the device,
233 * the same userspace process reads the corresponding result.
234 * Therefore, we increment a refcount on opening the device, so that
235 * only one process can communicate with the EC at a time.
236 *
237 * Return: 0 on success, or negative error code on failure.
238 */
telem_open(struct inode * inode,struct file * filp)239 static int telem_open(struct inode *inode, struct file *filp)
240 {
241 struct telem_device_data *dev_data;
242 struct telem_session_data *sess_data;
243
244 /* Ensure device isn't already open */
245 dev_data = container_of(inode->i_cdev, struct telem_device_data, cdev);
246 if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
247 return -EBUSY;
248
249 get_device(&dev_data->dev);
250
251 sess_data = kzalloc(sizeof(*sess_data), GFP_KERNEL);
252 if (!sess_data) {
253 atomic_set(&dev_data->available, 1);
254 return -ENOMEM;
255 }
256 sess_data->dev_data = dev_data;
257 sess_data->has_msg = false;
258
259 stream_open(inode, filp);
260 filp->private_data = sess_data;
261
262 return 0;
263 }
264
telem_write(struct file * filp,const char __user * buf,size_t count,loff_t * pos)265 static ssize_t telem_write(struct file *filp, const char __user *buf,
266 size_t count, loff_t *pos)
267 {
268 struct telem_session_data *sess_data = filp->private_data;
269 struct wilco_ec_message msg = {};
270 int ret;
271
272 if (count > sizeof(sess_data->request))
273 return -EMSGSIZE;
274 memset(&sess_data->request, 0, sizeof(sess_data->request));
275 if (copy_from_user(&sess_data->request, buf, count))
276 return -EFAULT;
277 ret = check_telem_request(&sess_data->request, count);
278 if (ret < 0)
279 return ret;
280
281 memset(sess_data->response, 0, sizeof(sess_data->response));
282 msg.type = WILCO_EC_MSG_TELEMETRY;
283 msg.request_data = &sess_data->request;
284 msg.request_size = sizeof(sess_data->request);
285 msg.response_data = sess_data->response;
286 msg.response_size = sizeof(sess_data->response);
287
288 ret = wilco_ec_mailbox(sess_data->dev_data->ec, &msg);
289 if (ret < 0)
290 return ret;
291 if (ret != sizeof(sess_data->response))
292 return -EMSGSIZE;
293
294 sess_data->has_msg = true;
295
296 return count;
297 }
298
telem_read(struct file * filp,char __user * buf,size_t count,loff_t * pos)299 static ssize_t telem_read(struct file *filp, char __user *buf, size_t count,
300 loff_t *pos)
301 {
302 struct telem_session_data *sess_data = filp->private_data;
303
304 if (!sess_data->has_msg)
305 return -ENODATA;
306 if (count > sizeof(sess_data->response))
307 return -EINVAL;
308
309 if (copy_to_user(buf, sess_data->response, count))
310 return -EFAULT;
311
312 sess_data->has_msg = false;
313
314 return count;
315 }
316
telem_release(struct inode * inode,struct file * filp)317 static int telem_release(struct inode *inode, struct file *filp)
318 {
319 struct telem_session_data *sess_data = filp->private_data;
320
321 atomic_set(&sess_data->dev_data->available, 1);
322 put_device(&sess_data->dev_data->dev);
323 kfree(sess_data);
324
325 return 0;
326 }
327
328 static const struct file_operations telem_fops = {
329 .open = telem_open,
330 .write = telem_write,
331 .read = telem_read,
332 .release = telem_release,
333 .owner = THIS_MODULE,
334 };
335
336 /**
337 * telem_device_free() - Callback to free the telem_device_data structure.
338 * @d: The device embedded in our device data, which we have been ref counting.
339 *
340 * Once all open file descriptors are closed and the device has been removed,
341 * the refcount of the device will fall to 0 and this will be called.
342 */
telem_device_free(struct device * d)343 static void telem_device_free(struct device *d)
344 {
345 struct telem_device_data *dev_data;
346
347 dev_data = container_of(d, struct telem_device_data, dev);
348 kfree(dev_data);
349 }
350
351 /**
352 * telem_device_probe() - Callback when creating a new device.
353 * @pdev: platform device that we will be receiving telems from.
354 *
355 * This finds a free minor number for the device, allocates and initializes
356 * some device data, and creates a new device and char dev node.
357 *
358 * Return: 0 on success, negative error code on failure.
359 */
telem_device_probe(struct platform_device * pdev)360 static int telem_device_probe(struct platform_device *pdev)
361 {
362 struct telem_device_data *dev_data;
363 int error, minor;
364
365 /* Get the next available device number */
366 minor = ida_alloc_max(&telem_ida, TELEM_MAX_DEV-1, GFP_KERNEL);
367 if (minor < 0) {
368 error = minor;
369 dev_err(&pdev->dev, "Failed to find minor number: %d\n", error);
370 return error;
371 }
372
373 dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
374 if (!dev_data) {
375 ida_free(&telem_ida, minor);
376 return -ENOMEM;
377 }
378
379 /* Initialize the device data */
380 dev_data->ec = dev_get_platdata(&pdev->dev);
381 atomic_set(&dev_data->available, 1);
382 platform_set_drvdata(pdev, dev_data);
383
384 /* Initialize the device */
385 dev_data->dev.devt = MKDEV(telem_major, minor);
386 dev_data->dev.class = &telem_class;
387 dev_data->dev.release = telem_device_free;
388 dev_set_name(&dev_data->dev, TELEM_DEV_NAME_FMT, minor);
389 device_initialize(&dev_data->dev);
390
391 /* Initialize the character device and add it to userspace */;
392 cdev_init(&dev_data->cdev, &telem_fops);
393 error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
394 if (error) {
395 put_device(&dev_data->dev);
396 ida_free(&telem_ida, minor);
397 return error;
398 }
399
400 return 0;
401 }
402
telem_device_remove(struct platform_device * pdev)403 static void telem_device_remove(struct platform_device *pdev)
404 {
405 struct telem_device_data *dev_data = platform_get_drvdata(pdev);
406
407 cdev_device_del(&dev_data->cdev, &dev_data->dev);
408 ida_free(&telem_ida, MINOR(dev_data->dev.devt));
409 put_device(&dev_data->dev);
410 }
411
412 static const struct platform_device_id telem_id[] = {
413 { DRV_NAME, 0 },
414 {}
415 };
416 MODULE_DEVICE_TABLE(platform, telem_id);
417
418 static struct platform_driver telem_driver = {
419 .probe = telem_device_probe,
420 .remove = telem_device_remove,
421 .driver = {
422 .name = DRV_NAME,
423 },
424 .id_table = telem_id,
425 };
426
telem_module_init(void)427 static int __init telem_module_init(void)
428 {
429 dev_t dev_num = 0;
430 int ret;
431
432 ret = class_register(&telem_class);
433 if (ret) {
434 pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
435 return ret;
436 }
437
438 /* Request the kernel for device numbers, starting with minor=0 */
439 ret = alloc_chrdev_region(&dev_num, 0, TELEM_MAX_DEV, TELEM_DEV_NAME);
440 if (ret) {
441 pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
442 goto destroy_class;
443 }
444 telem_major = MAJOR(dev_num);
445
446 ret = platform_driver_register(&telem_driver);
447 if (ret < 0) {
448 pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
449 goto unregister_region;
450 }
451
452 return 0;
453
454 unregister_region:
455 unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
456 destroy_class:
457 class_unregister(&telem_class);
458 ida_destroy(&telem_ida);
459 return ret;
460 }
461
telem_module_exit(void)462 static void __exit telem_module_exit(void)
463 {
464 platform_driver_unregister(&telem_driver);
465 unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
466 class_unregister(&telem_class);
467 ida_destroy(&telem_ida);
468 }
469
470 module_init(telem_module_init);
471 module_exit(telem_module_exit);
472
473 MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
474 MODULE_DESCRIPTION("Wilco EC telemetry driver");
475 MODULE_LICENSE("GPL");
476